Darkstorm Zero
Master of all Decepticons
Originally posted by Surtur
EDIT: Also just out of curiosity..how do you know how much Magneto knew about his helmet?
He didn't.
The original helmet was made for Sebastian Shaw by his Russian contacts. He had it made after he recruited Emma Frost. Shaw was rather paranoid regarding psychics. He knew that there was a definite probability that other psionic mutants existed, and thus had the helmet made, which he tested with Emma to make sure it worked.
The specifics of the helmets construction, other than it was some sort of metallic substances/alloys were used, was not made known to the audience. However, this raises 2 possible ways for Apocalypse to have learned it.
#1:
Spoiler:
He either got it when he literally downloaded all the computerised information through the television and radiowave broadcasts earlier in the movie.
#2:
Spoiler:
Or he got the info when he highjacked Xavier and Cerebro psionically, and for a long time, he had access to the minds and thoughts of the entire global population.
In either event, it wouldn't be hard for him to learn of the structure of kryptonite through various human corporations like Lexcorp or STARLabs who routinely use and experiment with the stuff. Once he has that info, he doesn't need to learn human techniques of making the stuff, or locating more, as he can simply atomically create the stuff out of thin air, or emit it's unique radiation through his powers easily enough.